Capacitance - The Farad, The Unit Of Capacitance, Energy Storage In Capacitors, Capacitance And Alternating Current - Working voltage, The significance of capacitance
Capacitance is an electrical effect that opposes change in voltage between conducting surfaces separated by an insulator. Capacitance stores electrical energy when electrons are attracted to nearby but separate surfaces. The voltage across an unchanging capacitance value will stay constant unless the quantity of charge stored is changed.
If the voltage across a capacitor is increased until charges jump from one plate to the other, the capacitor will probably fail, either momentarily or permanently. Capacitors are rated to specify the maximum continuous voltage that can be applied across the dielectric before the capacitor will fail.
Capacitance, inductance, and resistance are the passive electrical properties affecting electrical circuits. Understanding capacitance is an essential part of the study of electricity and electronics.
Resources
Books
Asimov, Isaac. Understanding Physics: Light, Magnetism, and Electricity. Vol. II. Signet Books, The New American Library.
Bord, Donald J., and Vern J. Ostdiek. Inquiry Into Physics. 3rd ed. West Publishing Company, 1995.
Sear, Zemansky, and Young. College Physics. 6th ed. Addison-Wesley Publishing Company, 1985.
Additional Topics
An electrical component that introduces capacitance is called a capacitor. Practical capacitors may have as small a value as a few trillionths of a Farad or as large as several Farads. …
Work is performed to accumulate charge in a capacitor. Each additional electron stored must overcome the repelling force caused by the charge previously stored. Energy storage increases as the square of the voltage across a capacitor. This often considerable energy can be used later. Capacitors used as energy reservoirs can deliver powerful pulses of energy. A capacitor can discharge quickly then …
A capacitor effectively conducts alternating current even though electrons do not cross from one plate to other plate. Alternating current that appears to pass through a capacitor is actually, the charge and discharge current resulting from the constantly-changing voltage across the capacitor. An uncharged capacitor always appears as a short circuit because its voltage must equal zero when its sto…
In a direct-current circuit a series capacitor will permit only a single pulse of charging current when the circuit voltage is changed. The charging current in quickly falls to almost zero as a capacitor charges from a constant-voltage source. Capacitors are sometimes used in circuits to oppose direct current. They may block direct current while simultaneously passing a superimposed alternating cu…
Dielectrics are the insulating materials used between the conducting plates of capacitors. Dielectrics increase capacitance or provide better insulation between the plates. Dielectrics materials exhibit very little ability to conduct electric charge. Mylar, paper, mica, and ceramics are commonly-used dielectrics. When extremely-high capacitance is required, a thin film of aluminum oxide on etched …
Dielectric strength is the measure of a dielectric's ability to resist electric stress without losing its insulating capabilities. A high dielectric constant does not always correspond to high dielectric strength. Distilled water has a fairly high dielectric constant but it has poor dielectric strength. Water, therefore, is not a useful dielectric for capacitors because it breaks down too e…
Failed capacitors are a common cause of electronic-equipment breakdowns. When a capacitor's dielectric is destroyed the resulting short circuit may cause other components to fail. Capacitors also develop open circuits, causing the loss of the capacitance. Electrolytic capacitors are generally less reliable than other types, a tradeoff made to secure very-high capacitance in a small package.…
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